1. Field of Invention
The present invention relates to a frame unit for a bicycle and a method of manufacturing the same, and more particularly, to a frame unit for a bicycle which includes a head tube, a seat tube, a frame, and left and right stays and a method of manufacturing the same.
2. Description of Related Art
In general, a frame unit for a bicycle is a constituent component that forms an overall structure of a bicycle, and manufactured by mutually joining constituent components such as a head tube, a seat tube, a frame, and left and right stays.
Regarding the frame unit for a bicycle, allowing flexibility to provide various designs and secure rigidity for safety are core factors, and to this end, the respective manufacturers actively conduct researches on development of technologies, process methods, materials, and the like.
Recently, in order to implement various designs and secure rigidity for safety, materials such as aluminum, chromium-molybdenum steel, carbon, and titanium are used instead of a high tensile steel material that is generally used.
FIG. 1 is a configuration diagram of a frame unit for a bicycle according to the related art.
Referring to FIG. 1, a frame unit 100 for a bicycle of the related art includes a head tube 101, a seat tube 103, an upper frame 105, a lower frame 107, and upper and lower stays 109 and 111 disposed at both sides.
A steering shaft (not illustrated) to which a steering handle is connected is installed on the head tube 101, and a seat pipe (not illustrated) connected to a seat is installed on the seat tube 103.
The upper and lower frames 105 and 107 connect and support the head tube 101 and the seat tube 103.
Rear ends of both the upper and lower stays 109 and 111 are connected to each other so as to form a rotating body fork 113 to which a rear wheel is mounted.
A front end of the lower stay 111 is connected to a pedal assembly 115 that is configured at a lower end of the seat tube 103.
Meanwhile, the frame unit 100 for a bicycle mostly includes both the upper frame 105 and the lower frame 107, but in some cases, only a single frame, that is, only the upper frame 105 may be applied between the head tube 101 and the seat tube 103.
However, according to the frame unit 100 for a bicycle of the related art, which has the aforementioned configuration, when the head tube 101, the seat tube 103, the upper frame 105, the lower frame 107, and the upper and lower stays 109 and 111 are joined to each other by a welding process, residual stress due to welding heat is distributed to joining portions. Particularly, impact loads are directly applied when the bicycle runs, thereby causing a serious problem with respect to safety such as cracks or damage occurring at the periphery of the joining portions.
Particularly, because welding work is performed after the head tube 101 passes through a separate preheating process in accordance with a difference in thickness between the upper and lower frames 105 and 107 when the head tube 101 is joined to the upper and lower frames 105 and 107, there is a drawback in that a welding defect occurs if the preheating process is not properly performed.
In addition, since the process of welding the joining portions is manually performed, an inferiority rate is high because there is a difference in welding quality in accordance with skill of workers and working environment, and thereby, there are drawbacks in that an excessive working time is required and productivity deteriorates.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.